... did you try both ROM sets from my machines as they were physically dumped as opposed to read out by BASIC... the disk manual states the boot priority:

a. If a module is inserted, it's loaded when the PC is switched on or reset.b. If there is no module, but a ready disk station, the disk is loaded. If there is no disk inserted, the system waits for the correct insertion of a disk.c. If neither a. nor b. are true, the system loads the internal BASIC interpreter.

... Bit 0 of IN 10H tells you if a Floppy unit is available (=1) or not ...

Mounting a known good disk image in B: gives you an error message from the Alphatronic:

Another thing I'd suggest is to set the number of disk drives to two - the F2 extension drive has no provision for a passthrough to a third or fourth drive.If you search for pictures of the system, it's almost always a stack of the F1 and F2 drives.